Originally Posted by Andrew R Stewart

Well actually...

Shimano dual pivot brake calipers have has a caliper return spring adjuster for a long time and on most all their series/grades. No screw but a small plastic block that most here likely think is a low friction pad. The plastic block has a thin (the usual OEM setting) and a thick side. By rotating the block 180* the spring is preloaded more, by the added thickness of the block as it nestles back into the arm's tab. These plastic blocks are one of the first things to lose if the spring is detached from the arm. The spring acts as a catapult and flings the "unseen" block across the room. Andy